Unibus

From Trammell Hudson's Projects

Unibus Adapter

I'm building an adapter from the BeagleBone Black to the DEC Unibus to allow modern CPUs to interface with Unibus devices, or to emulate other devices on the bus, like a network adapter for our PDP-11. There are 56 signals on the bus and the BBB has 55 user GPIO lines, but the DCLO line isn't really necessary since by the time it is asserted it is too late to do anything about it.

Board, schematic and OSH Park link, although they are untested yet. They also have a wrong package for the resistor array and a bad pinout for the MOSFET level shifters, so don't order them!

PCB details

The 3.3V BeagleBone is interfaced to the 5V open-collector bus using the technique described in NXP appnote 10441. Due to a mistake in the board layout, the pullup resistor array is the wrong package, but this can be worked around by using the ARM's pullups. Additionally, the MOSFET package has the two drain pins swapped, so the input to the BeagleBone's GPIO is scrambled. This can be fixed by software, but means that the LEDs aren't meaningful.